Problem: $3r - 9s + 10t + 3 = -10s + 7t - 10$ Solve for $r$.
Combine constant terms on the right. $3r - 9s + 10t + {3} = -10s + 7t - {10}$ $3r - 9s + 10t = -10s + 7t - {13}$ Combine $t$ terms on the right. $3r - 9s + {10t} = -10s + {7t} - 13$ $3r - 9s = -10s - {3t} - 13$ Combine $s$ terms on the right. $3r - {9s} = -{10s} - 3t - 13$ $3r = -{s} - 3t - 13$ Isolate $r$ ${3}r = -s - 3t - 13$ $r = \dfrac{ -s - 3t - 13 }{ {3} }$